The seismographic data, as well as historical resources are indicative of the occurrence of numerous earthquakes in the region of Garmsar since the prehistoric centuries. The 4th century BC earthquake in the region of Caspian Gate and Eivankey City with the magnitude of Ms = 7.9 and intensity of Io = X and also the earthquake of spring 743 AD, (Spring 122 Hegira, Solar year)estimated at the magnitude of Ms= 7.2 and intensity of Io = VIII in the region of Sardarreh Khar (Caspian Gate) and Takhte-Rostam Mountain, and earthquakes of Moharram 1367(3th of September, 1988) continuing for one year, inspired the author to investigate and introduce the causing factors of these earthquakes.
In this research, it has been identified that on one hand factors such as activation of certain unknown faults.The geographical distribution of the seismological focus properly indicate Garmsar,s fault activation and the faults of Rude-Shur valley, Ejdeha Mountain and the faults of north and south part of Kalarz Mountain and Red Mountain, Rameh, Ghalibaf, Gach-ab and Gugerd Mountain faults have been acted in the past history of this region (Fig. 2).